This report summarizes observations of 127 patients who underwent pulmonic valvulotomy for valvular pulmonic stenosis with intact ventricular septum and without obstruction to left ventricular inflow or outflow. Of the 127 patients, 30 (24%) preoperatively by dye-dilution curves had shunting at the atrial level: in 19 (63%), the shunt was right to left and in the other 11 (27%), entirely left to right. The patients with right-to-left interatrial shunts had severe pulmonic valve stenosis (average peak systolic pressure gradient plus 120 plus 11 mm Hg) and small (average diameter 1.1 plus or minus 0.1 cm) sized defects in the atrial septum (patent foramen ovale). In contrast, the patients with left-to-right shunts had mild to moderate pulmonic valve stenosis (average peak systolic pressure gradient equals 60 plus 5 mm Hg) and relatively large (average diameter equals 2.8 plus or minus 0.1 cm) defects in the atrial septum (true atrial septal defect).